Change in the Use of Fractionation in Radiotherapy Used for Early Breast Cancer at the Start of the COVID-19 Pandemic: A Population-Based Cohort Study of Older Women in England and Wales

•Publication of trial results and RCR guidance aligned to encourage use of radiotherapy in five fractions over one week.•Use of 26Gy5F in women (aged 50+ years) with breast cancer increased from <1% in Feb-2020 to 70% in Apr-2020.•Among >5000 women receiving postoperative radiotherapy from April-July 2020, nearly three-quarters had 26Gy5F radiotherapy.•The increase was uniform for all women (aged 50+ years) whose tumour features matched guidance dose selection criteria.